Operator compartments for modern work vehicles are often enclosed with large glass or plastic panels that extend substantially the entire way around the operator. The large panels enclose the operator and protect the operator from the elements. The panels define operator compartments that are significantly larger than the compartments of automobiles.
This large internal volume and expanse of transparent panels makes the operator compartment (or “cabin”) function like a greenhouse. When a work vehicle is turned off and left in bright sunlight, even for a short time, the compartment can heat to over 50 degrees C. This solar heating is compounded by engine and transmission heat, which can be substantial as well.
The first thing most operators do on entering a work vehicle on a hot summer's day is to turn the air conditioner on full blast until the operator compartment temperature is bearable. Given the size of the operator compartment and heat loading from the sun, this can take a while.
Work vehicles may have a pressurizer blower, which can make them even more difficult to cool. Vehicles such as tractors or combines have two blowers, one blower for pressurizing the operator compartment with outside air and the other blower for recirculating air within the operator compartment.
The purpose of the pressurizer blower is to provide a slight positive pressure in the operator compartment. This ensures that no air is sucked into the operator compartment through cracks are gaps in the ceiling, walls, or floor of the operator compartment. This positive pressure is about 6 to 25 mm of water, which is enough to prevent dirty, dusty air from infiltrating into the compartment, dirtying seats and possibly fouling operator controls.
Since an older vehicle may have many small air leaks located around the compartment, a pressurizer blower may blow a significant amount of hot outside air into the operator compartment to maintain a slight positive pressure inside the compartment.
Therefore, when the operator mounts the vehicle and turns the air conditioner on, he is not only cooling down the heated interior of the operator compartment, he is also cooling down all the hot air introduced by the pressurizer blower. This delays the initial cool-down of the vehicle.
Reviewing this problem, the applicants discovered that even with the pressurizer blower disabled, a slight positive pressure can be maintained in the operator compartment by running the cabin recirculation blower at its maximum speed. At this speed, the recirculation blower draws sufficient amount of fresh air into the cab to provide minimum cab pressurization of 6 mm of water needed to protect the cab from dust ingress. Thus, it was possible to turn the pressurizer blower off, thereby reducing the amount of hot air drawn into the operator compartment during initial cool-down of the operator compartment or during extreme conditions when the vehicle is exposed to high heat loads.
What is needed, therefore, is an HVAC system for work vehicle that prevents the pressurizer blower from blowing hot air into the operator compartment during initial cool-down or extreme conditions. What is also needed is a system for reducing the output of the pressurizer blower when the operator selects high output from the air-conditioning system. What is further needed is an HVAC system that automatically senses when the operator wants high output from the vehicle air-conditioning system and automatically reduces the output of the pressurizer blower. These and other objects are satisfied by the invention described below.